grafana: add minecraft server stats

hosts/muffin/service-configs.nix

@@ -196,6 +196,10 @@ rec {
         port = 9563;
         proto = "tcp";
       };
+      minecraft_exporter = {
+        port = 9567;
+        proto = "tcp";
+      };
       prometheus_zfs = {
         port = 9134;
         proto = "tcp";

lib/overlays.nix

@@ -75,4 +75,19 @@ final: prev: {
     '';
     meta.mainProgram = "igpu-exporter";
   };
+
+  mc-monitor = prev.buildGoModule rec {
+    pname = "mc-monitor";
+    version = "0.16.1";
+    src = prev.fetchFromGitHub {
+      owner = "itzg";
+      repo = "mc-monitor";
+      rev = version;
+      hash = "sha256-/94+Z9FTFOzQHynHiJuaGFiidkOxmM0g/FIpHn+xvJM=";
+    };
+    vendorHash = "sha256-qq7rIpvGRi3AMnBbi8uAhiPcfSF4McIuqozdtxB5CeQ=";
+    # upstream tests probe live Minecraft servers
+    doCheck = false;
+    meta.mainProgram = "mc-monitor";
+  };
 }

services/grafana/dashboard.nix

@@ -687,6 +687,188 @@ let
           overrides = [ ];
         };
       }
+
+      # -- Row 6: Minecraft --
+      {
+        id = 14;
+        type = "stat";
+        title = "Minecraft Players";
+        gridPos = {
+          h = 8;
+          w = 6;
+          x = 0;
+          y = 40;
+        };
+        datasource = promDs;
+        targets = [
+          {
+            datasource = promDs;
+            expr = "sum(minecraft_status_players_online_count) or vector(0)";
+            refId = "A";
+          }
+        ];
+        fieldConfig = {
+          defaults = {
+            thresholds = {
+              mode = "absolute";
+              steps = [
+                {
+                  color = "green";
+                  value = null;
+                }
+                {
+                  color = "yellow";
+                  value = 3;
+                }
+                {
+                  color = "red";
+                  value = 6;
+                }
+              ];
+            };
+          };
+          overrides = [ ];
+        };
+        options = {
+          reduceOptions = {
+            calcs = [ "lastNotNull" ];
+            fields = "";
+            values = false;
+          };
+          colorMode = "value";
+          graphMode = "area";
+        };
+      }
+      {
+        id = 15;
+        type = "stat";
+        title = "Minecraft Server";
+        gridPos = {
+          h = 8;
+          w = 6;
+          x = 6;
+          y = 40;
+        };
+        datasource = promDs;
+        targets = [
+          {
+            datasource = promDs;
+            expr = "max(minecraft_status_healthy) or vector(0)";
+            refId = "A";
+          }
+        ];
+        fieldConfig = {
+          defaults = {
+            mappings = [
+              {
+                type = "value";
+                options = {
+                  "0" = {
+                    text = "Offline";
+                    color = "red";
+                    index = 0;
+                  };
+                  "1" = {
+                    text = "Online";
+                    color = "green";
+                    index = 1;
+                  };
+                };
+              }
+            ];
+            thresholds = {
+              mode = "absolute";
+              steps = [
+                {
+                  color = "red";
+                  value = null;
+                }
+                {
+                  color = "green";
+                  value = 1;
+                }
+              ];
+            };
+          };
+          overrides = [ ];
+        };
+        options = {
+          reduceOptions = {
+            calcs = [ "lastNotNull" ];
+            fields = "";
+            values = false;
+          };
+          colorMode = "value";
+          graphMode = "none";
+        };
+      }
+      {
+        id = 16;
+        type = "timeseries";
+        title = "Minecraft Player Activity";
+        gridPos = {
+          h = 8;
+          w = 12;
+          x = 12;
+          y = 40;
+        };
+        datasource = promDs;
+        targets = [
+          {
+            datasource = promDs;
+            expr = "sum(minecraft_status_players_online_count) or vector(0)";
+            legendFormat = "Online players";
+            refId = "A";
+          }
+          {
+            datasource = promDs;
+            expr = "max(minecraft_status_players_max_count) or vector(0)";
+            legendFormat = "Max players";
+            refId = "B";
+          }
+        ];
+        fieldConfig = {
+          defaults = {
+            unit = "short";
+            min = 0;
+            decimals = 0;
+            color.mode = "palette-classic";
+            custom = {
+              lineWidth = 2;
+              fillOpacity = 15;
+              spanNulls = true;
+            };
+          };
+          overrides = [
+            {
+              matcher = {
+                id = "byFrameRefID";
+                options = "B";
+              };
+              properties = [
+                {
+                  id = "custom.lineStyle";
+                  value = {
+                    fill = "dash";
+                    dash = [
+                      8
+                      4
+                    ];
+                  };
+                }
+                {
+                  id = "custom.fillOpacity";
+                  value = 0;
+                }
+                {
+                  id = "custom.lineWidth";
+                  value = 1;
+                }
+              ];
+            }
+          ];
+        };
+      }
     ];
   };
 in

services/grafana/exporters.nix

@@ -10,6 +10,9 @@ let
   jellyfinExporterPort = service_configs.ports.private.jellyfin_exporter.port;
   qbitExporterPort = service_configs.ports.private.qbittorrent_exporter.port;
   igpuExporterPort = service_configs.ports.private.igpu_exporter.port;
+  minecraftExporterPort = service_configs.ports.private.minecraft_exporter.port;
+  minecraftServerName = service_configs.minecraft.server_name;
+  minecraftServerPort = service_configs.ports.public.minecraft.port;
 in
 {
   # -- Jellyfin Prometheus Exporter --
@@ -109,4 +112,45 @@ in
       REFRESH_PERIOD_MS = "30000";
     };
   };
+
+  # -- Minecraft Prometheus Exporter --
+  # itzg/mc-monitor queries the local server via SLP on each scrape and exposes
+  # minecraft_status_{healthy,response_time_seconds,players_online_count,players_max_count}.
+  # mc-monitor binds to 0.0.0.0 (no listen-address flag); the firewall keeps
+  # 9567 internal and IPAddressAllow pins the socket to loopback as defense-in-depth.
+  systemd.services.minecraft-exporter =
+    lib.mkIf (config.services.grafana.enable && config.services.minecraft-servers.enable)
+      {
+        description = "Prometheus exporter for Minecraft (mc-monitor SLP)";
+        after = [
+          "network.target"
+          "minecraft-server-${minecraftServerName}.service"
+        ];
+        wantedBy = [ "multi-user.target" ];
+        serviceConfig = {
+          ExecStart = "${lib.getExe pkgs.mc-monitor} export-for-prometheus";
+          Restart = "on-failure";
+          RestartSec = "10s";
+          DynamicUser = true;
+          NoNewPrivileges = true;
+          ProtectSystem = "strict";
+          ProtectHome = true;
+          PrivateTmp = true;
+          MemoryDenyWriteExecute = true;
+          RestrictAddressFamilies = [
+            "AF_INET"
+            "AF_INET6"
+          ];
+          IPAddressAllow = [
+            "127.0.0.0/8"
+            "::1/128"
+          ];
+          IPAddressDeny = "any";
+        };
+        environment = {
+          EXPORT_SERVERS = "127.0.0.1:${toString minecraftServerPort}";
+          EXPORT_PORT = toString minecraftExporterPort;
+          TIMEOUT = "5s";
+        };
+      };
 }

services/grafana/prometheus.nix

@@ -95,6 +95,12 @@ in
           { targets = [ "127.0.0.1:${toString service_configs.ports.private.igpu_exporter.port}" ]; }
         ];
       }
+      {
+        job_name = "minecraft";
+        static_configs = [
+          { targets = [ "127.0.0.1:${toString service_configs.ports.private.minecraft_exporter.port}" ]; }
+        ];
+      }
       {
         job_name = "zfs";
         static_configs = [